Conventionally, electric power conversion devices are known that perform electric power conversion using a switching element and transmit electric power between an input and an output via a transformer. For example, a bidirectional DC/DC converter that transmits DC power bi-directionally is disclosed in JP 2011-234541 A (hereinafter referred to as “Document 1”) as this type of electric power conversion device. The electric power conversion device described in Document 1 is provided with a primary circuit and a secondary circuit that sandwich a transformer.
The primary circuit and the secondary circuit each include a bridge circuit configured by a reverse conducting type semiconductor switch (switching element). The electric power conversion device can transmit desired DC power bi-directionally by controlling duty cycles (on duties) of the switching element of the primary circuit and the switching element of the secondary circuit.
Incidentally, although the electric power conversion device described in Document 1 can transmit desired DC power between the primary circuit and the secondary circuit by controlling the duty cycles of the switching elements, a voltage ratio between an input voltage and an output voltage depends on the winding ratio of the transformer. That is, the electric power conversion device described in Document 1 cannot output voltage by boosting the input voltage and only performs current adjustment, since bridge circuits are used in the primary circuit and the secondary circuit, and only the duty cycles are controlled.
On the other hand, an electric power conversion device that is used for utilizing electric power of a storage battery that is mounted in an automobile having an electric motor serving as a power source, a storage battery used by being attached to a building, or the like is required to have a function of adjusting a relationship between an input voltage and an output voltage over a wide range.